This kind of illumination apparatus has a structure in which a holding member made of a material having elasticity and heat resistance, such as a white or ivory yellow silicone rubber, holds glass tube portions near the terminals of a flash discharge tube that is a light source. This is for preventing a breakage of the flash discharge tube caused by the direct transmission of external force (impact strength) acting on the illumination apparatus to the flash discharge tube when the holding member is not an elastic member but a rigid member. This is also for avoiding troubles caused by deformation or alteration of the holding member made of a material with a low heat resistance when the portions near the terminals of the flash discharge tube have high temperatures due to continuous emission of light.
On the other hand, an illumination optical system requires maintenance of optical characteristics even if its orientation is changed and external impact strength acts on it. For this, it is necessary to keep the positional relationship between the light source and the optical member with accuracy, and the elasticity of the holding member plays an important role in keeping this positional relationship. In other words, keeping the positional relationship is generally performed by bringing the flash discharge tube in contact with positioning dowels formed on a reflector and using pressing force or repulsive force generated by the silicone rubber. This intends to properly keep the positional relationship between the light source and optical member to maintain the optical characteristics by utilizing the elastic force generated in the silicone rubber (see Japanese Patent Laid-Open application No. 2003-222941).
The method for holding the light source in the conventional illumination apparatuses is thus devised to satisfy mechanical requirements such as holding structures preventing breakages of the light source, measures against heat generating from the light source, and accurate positioning between the light source and the optical member.
However, in the conventional illumination apparatuses, though light rays from the light source directly impinge on the holding member, these light rays are not used positively as illumination light. In other words, since the luminous flux from the light source includes many unused components, the conventional illumination apparatuses are not necessarily efficient.
Furthermore, since the positional relationship between the light source and the optical member is kept not by the direct contact thereof with each other, but by the intervention of the holding member having a manufacturing tolerance, the setting of the positional relationship is not necessarily accurate.
Moreover, using the holding member that is a member separate from the optical member increases the number of constituent members of the illumination apparatus.